Prior Art Cable and Reel Systems
Prior art lift task exercise systems which employ a cable and cable reel system for controlling the exercise motion typically have a fixed cable outlet point. A cable reel with a cable carried thereon extends through an exit point in a floor mat with the free end of the cable attached to a human interface mechanism which is typically a handle or a pair of handles separated by a bar. A resisting system for driving and/or resisting rotation of the cable reel may be either a passive isokinetic type of accommodating resistance mechanism or it may be an active servo motor drive and control system. In the case of a passive resistance system, a separate mechanism is required for returning the cable to the lowered position. In the latter case, the active system can reel in the cable.
Prior art systems of this type have limited capability of accurately measuring and controlling lift task parameters such as cable tension to imitate a real life lifting task. They are accurate only if the movement of the handle is in a substantially vertical direction. In other words, cable tension is only equivalent to a free weight being lifted if the cable is maintained in a substantially true vertical orientation.
When the cable direction is substantially altered from the vertical direction, the cable tension resolves into a vertical component corresponding to perceived "box" weight and a horizontal component perceived by the person as a sideways movement restraint. The person will thus sense that the handle is tethered to a fixed point on the platform and is not only resisting the lift of the handle but also the forward movement thereof. Thus this type of prior art system is incapable of accurately imitating a typical real life lift task of picking up a weighted box and setting it on a shelf. The change in orientation of the cable as the handle is moved forward to set it on a shelf produces change in the perceived "box" weight and places other forces on the person that are not the same as lifting and placing an actual weighted box on the shelf.
The resisting system of the prior art also do not control cable tension in a way that imitates the inertial effects of accelerated motion of the "box." Typically, isokinetic resistance is offered to movement of the handle and this does not simulate the forces actually experienced by the muscle and bone structure of a person as they lift a box. Box is used in quotes here, because the system of the prior art also do not use an actual box as the human interface mechanism and thus do not simulate the aspect of a lift task that involves the actual positioning of hands and fingers thereon around the type of object that is actually used in the lift task being simulated.
The prior art systems are thus unable to simulate accurately the actual lift tasks that workers perform. They are not capable of providing a basis for accurately assessing the capability of a worker to do particular lifting and placing tasks. Furthermore they do not provide a basis for accurately training persons in performing a variety of lift tasks.
An additional disadvantage with this type of prior art system is that the fixed cable outlet point can interfere with the natural movement of the feet of the person performing the lift task and could in some circumstances create a tripping hazard.